The present invention relates to a fuel tank having separate inlet and outlet connections and to be provided for storing aggressive liquids such as used for example in propulsion systems for space vehicles, satellites or the like. In particular the inventive fuel tank is to operate in a gravity free environment.
It is well-known that satellites when orbitting require a particular orientation relative to the earth. This orientation is usually needed so that the satellite can perform the desired tasks and, most importantly, can continue to communicate with ground stations. Therefore, it is known to provide satellite and orbitting space vehicles with attitude position and orientation controls which permit the correction and maintaining of particular positions in all directions of freedom of motion. Generally, one uses mini-propulsion systems and small jets for that purpose which provide very small but very accurately metered mechanical impulses so that the requisite control and corrective motion can be obtained.
The miniature or mini-propulsion systems and control jets in a space vehicle require a certain amount of fuel and, therefore, it is necessary to store such fuel in a suitable container within the satellite. The fuel used here are usually in the liquid state and are passed through a gas generator for immediate and direct ejection by and from the propulsion system. It is necessary to provide the fuel transfer from the tank to the propulsion system in a very accurate manner, and in particular it is necessary to limit the amount of fuel transferred to the exact amount that is needed for the generation of a particular pulse and moment. In particular, gas bubbles must not be included in the fuel. This requirement arises primarily because the transfer of the fuel from the tank requires by itself a propulsion or, better, driving gas. This driving gas must be carefully separated from the fuel proper as they must not mix. The liquid fuel and the driving gas may not physically blend, but the absence of gravity precludes natural stratification. It can readily be seen that in case of gas bubbles included in the fuel, the metered quantity may be faulty as to the precise amount of fuel provided for the propulsion system. For this reason, it has been proposed to divide the interior of the fuel tank by means of a synthetic membrane which separates a compartment containing the driving gas with certainty from the compartment containing the fuel proper. Such construction is workable in principle, but not necessarily in all specific instances.
A known and conventionally used single component fuel is for example, hydrazine. Decomposing hydrazine constitutes a very useful propulsion gas that can be used directly by the propulsion system for purposes of position and attitude control as mentioned above. Multi-component fuel is also known which type of fuel is often preferred because of a somewhat larger energy content, and for this reason multi-component fuel is more suitable, particularly in those cases in which the space vehicle cannot be refueled frequently (or not at all). However, it is a significant drawback of these multi-component fuels that at least some components are highly chemically aggressive. A typical example here is nitrogentetraoxide. The aggressiveness of this component renders impossible the utilization of synthetic membranes in the tank particularly when it is expected that the membrane may be exposed to this (or other) aggressive components for a long period of time.
In order to avoid the problem of chemical aggression, fuel tanks have been proposed which, for example, utilize the surface tension of liquid for purposes of transporting the liquid from the tank to the propulsion system. One still needs, however, a driving gas, and if the fuel is not physically separated from the driving gas there is still the danger that gas bubbles pass into and through the fuel and again the propulsion system will no longer be reliable.